FIELD OF THE INVENTION
The invention relates to a switching stage having a differential amplifier configuration; an emitter follower transistor connected downstream thereof; a current source connected between the emitter of the emitter follower transistor and a terminal for a first supply potential; an output; a resistor with a first terminal connected to the emitter of the emitter follower transistor and a second terminal connected to the output; and a terminal for a second supply potential being connected to the collector of the emitter follower transistor.
Such switching stages are used, for instance, as output drivers in integrated circuits made by the current switch technique. The output of the switching stage is connected to one end of a signal line that is disposed on a printed wiring board. The other end of the signal line is connected to the base of an input transistor of a further switching stage. Upon a changeover, a current flows through the resistor, and due to this current the capacitors of the signal line are inversely charged. At the transition from a low level to a high level, the current flows through the resistor from the emitter of the emitter follower transistor to the output of the switching stage. At the transition from a high to a low level, the current flows in the opposite direction. In the first instance, the current is furnished by the emitter follower transistor, which additionally carries the current impressed by the current source. In the second instance, the current flows through the resistor through the current source. Since the current source continuously furnishes the current impressed by it, in other words during the state of repose of the switching stage as well, the power loss is high.